When operating printing machines in various printing modes, it is frequently necessary to readjust the quantity of ink which is being supplied from an ink supply source to the plate cylinder of the printing machine. Lithographic printing machines which are operable either in the offset mode of printing or for di-litho printing require differences in the thickness of the ink film supplied by the inker. For offset printing, a very thin layer of ink is desirable and suitable. The ink is transferred from the plate cylinder to a somewhat yielding blanket or rubber cylinder, and thus ink will be supplied to all areas of paper which is to be printed, being capable of entering even small depressions and pores of the paper due to the yielding nature of the rubber blanket cylinder. In di-litho printing, however, ink is supplied from the hard plate directly to the ink-receiving web on which printing is to be carried out, typically paper. Di-litho printing thus requires a thicker layer of ink, particularly if paper is to be printed on which does not have a smooth surface. The yielding rubber surface of the blanket cylinder is not available, and print, directly, must be supplied from the hard plate to the paper. Thin layers of ink thus may not reach all depressions within the paper surface so that the printed subject matter may not be completely transferred from the plate cylinder, as desired.
In order to accomodate different printing modes, it has previously been the practice to readjust the doctor blade of an ink supply system for the different types of printing modes to be accomodated by the printing machine. It is difficult to readjust the doctor blade, and to obtain a precise positioning thereof after readjustment, and, for example at a later date, to again reposition the blade to establish a previously used ink film.
Usually, inkers have a plurality of serially arranged ink transport rollers, some of which may be oscillating or milling rollers, to provide an ink roller train, in which the ink is, at the end, applied to one or more ink application rollers which are in contact with the plate cylinder. An inker of this type is shown, for example, in German Examined Published Application DE-AS No. 27 03 425 of which U.S. Pat. No. 4,148,256, by the inventor hereof corresponds.